1. Field of the Invention
The present invention relates to management of file systems, in particular, to management of files by virtualizing file systems created in a storage.
2. Description of the Related Art
Recently, there have been increased needs for file service using file management system including a file server or servers (NAS: Network Attached Storage) for managing file systems and more than one storage for storing files of the file systems. In order to meet such needs, there have been increased capacities of a storage for storing files, and more disk devices have been required for building up the storage. As more disk devices are required, more power consumption is required for the entire storages. In particular, increase of power consumption of the entire storages is a big problem for a high-capacity disk array system constituting RAID (Redundant Array of Inexpensive Disks) by using plural disk devices.
JP 2007-86843 A discloses a technique to store metadata on a cache memory before a pin-down operation of HDD (Hard Disk Drive) corresponding to logical volumes on which file systems are created, so as to enable it to refer to file attributes even if the HDD is being spun down, and then start a spin-up operation of the logical volumes, triggered by a reference to this stored metadata, thereby to prevent delay of access response as well as to realize power saving of the entire storage.
However, even such a technique disclosed in JP 2007-86843 A cannot spin down HDD corresponding to logical volumes on which file systems are created if a user accesses even one of plural files managed by a file system. This means that no power saving can be expected under an environment of continuous file accesses.
The present invention has an object to realize power saving even under such an environment of continuous file accesses.